Epilog cuts weak in lower right quadrant

[Steve Stram]

I have use of three Epilog Helix 60w lasers. They are in a community shop and people cut nearly anything with them even though there is a list of things not to cut. Lot of rastering is done also on the machines.

I have been cutting 1/4" Baltic Birch (interior glue) at 16 speed, 90% power and 500 hz. The cutting is of 4" square geometry nested on the 18" x 24" table. Of the 24 identical parts, the upper left cut just fine and fall out when the board is lifted. As it get to the far right the cut is less through with the bottom ones in the lower right not even having a mark on the back of the sheet.

There have been many "explanations" from the shop management; board is warping (not), part of the mirror is worn out, fumes have made part of the mirror less useful,...

I experimented with putting 6" squares of the same 1/4" ply material in the four corners and center. This was to take out the warping due to heat argument. The results showed the lower right having incomplete penetration while the upper left cut completely through.

Any ideas on the cause and cure?

Steve.

[Isaac Clarke]

I don't own an epilog, but whenever I have the same fault its usually mirror alignment issues

[John Pletcher]

I agree with Isaac, I would check the optical alignment. Place the target that comes with the machine into the optical head on the gantry, turn x/y off, turn on the red dot pointer and see where on the target the red dot falls when the head is in the different corners. I suspect you will find the red dot in corner 4 is out of the optimal sweet spot. I think an optical alignment will fix your problem

[Glen Monaghan]

Could be mirror alignment problem, or perhaps the table isn't leveled/parallel with the carriage so the distance from lens to substrate is enough different in that corner that the beam is too far out of focus to cut through there. The latter can be checked easily with power off by manually moving the head to the four corners and measuring from bed to head to see if that corner is significantly off. Test mirror alignment with Epilog's published procedure.

[Braden Todd]

If alignment looks good, I would check the mirrors and make sure they're not fried. The lower right side is the furthest point the beam has to travel so that would make sense that the wood isn't cut the whole way, you may be losing power in a mirror that's bad or not aligned.

Good luck!

[Steve Stram]

Thanks for all the advise.

The shop tech has checked the optical alignment using the circle fixture while I was there and it was "within spec". Not sure what not being in the exact center would cause, but this seems more severe performance.

I'm from a CNC world and have minimal knowledge of a Laser. The tech has mentioned the mirror being fried, but I didn't really understand what that means.

How about a little Mirror 101 for a new guy, is the mirror reflective material eroded and the beam not transferring the full energy, is changing a mirror complicated, expensive, time consuming, can fumes from cutting improper things be a culprit, what is the normal life of a mirror???

Steve.

[Joe Pelonio]

When you clean your mirrors and lenses you inspect them closely. Bad ones will show a worn spot on the gold, or tiny cracks that you can see with your eyes. I would propose another possibility, from past experience. If the mirrors, lenses and focus are good, and it cuts the closest best, farthest worse on only one machine, your beam may just be getting weaker as the tube reaches the end of it's life. Typically you would continue cutting using only the left half until it requires more power/slower speed, and then order a new tube.

[Larry Bratton]

Braden, I beg to differ as to the lower right being the furthest point from the beam. Lower left, standing in front of the machine or Position 4 is it. However, I would suggest a through cleaning of the mirrors, and be sure not to overlook Mirror #1 which is at the back of machine, down low. You have to remove the back panel to get to it. If you remove all the mirrors then you will have to do an alignment. Here is where the #1 mirror is located.Mirror 1.JPG

If alignment looks good, I would check the mirrors and make sure they're not fried. The lower right side is the furthest point the beam has to travel so that would make sense that the wood isn't cut the whole way, you may be losing power in a mirror that's bad or not aligned.

Good luck!

[Steve Stram]

Typically you would continue cutting using only the left half until it requires more power/slower speed, and then order a new tube.

That is my plan until it gets corrected.

Of the three lasers, one just had the tube replaced and is giving me the worst results. It may be that one needs a mirror.

Steve.

[Larry Bratton]

It hasn't been aligned properly if the optics are good and are clean. What your speaking of is Position #2 and is controlled by Mirror 2, top right rear.

That is my plan until it gets corrected.

Of the three lasers, one just had the tube replaced and is giving me the worst results. It may be that one needs a mirror.

Steve.

[Braden Todd]

That's true for an EXT but he is using a Helix and the beam comes from the other side of the machine.

[Larry Bratton]

Hey..thanks for correcting me. I assumed (and you know what happens when you ass u me) that they were all set up the same way,having not ever run a Helix. Actually makes more sense for the beam to originate on the left side than the right, as users just tend to put their work in the upper left, I know we do. Many times, if I have something I need max power on I move it to top right on the Ext.

[Kev Williams]

Ummm... If Steve is cutting multiple squares on the table, in various places on the table, and only the lower right corners of the SQUARES are not cutting, as opposed to towards the lower right corner of the TABLE, then how can it be mirror alignment? If it was, anything farther down and right of the last corner that didn't cut would ALL get worse, not just the lower-right again.

However, mirror mis-alignment could be caused "on the fly" if one of the long gantry drive belts is loose or damaged. It could cause the entire gantry to twist slightly, which would change the position of the beam on the mirrors...

Question for Steve-- Have you tried reversing the direction of the cut to see what happens? Or the starting point of the cut?

[Vince Iorio]

I have used an Epilog before (not sure of the model number) and have seen a similar problem. My solution was to increase the power. I believe the cause of the problem is that the table is not parallel with the guide ways of the mirrors. The manual had a section in it that tells you how to align the table, and it did not look to be to hard (though increasing the power was easier). A quick test would be to manually focus the laser at a point in the lower right where it is not cutting through. If it cuts in this section after using it for focusing, and not in the upper left, then the problem is the alignment.

Vince

[Ronald Erickson]

I agree with Glen in post #4: If the table is not level / parallel to the lens at every position of the gantry and the distance from the lens to the table is significantly changing in the lower right corner, then the focus would change and create an issue.

Steve (OP), when you did the test of the four corners with the 6" squares of 1/4" thick ply, where did you focus each piece? Did you focus each test piece individually at their respective corners of the table before cutting them (and refocus for each piece at each corner)? Or did you focus the laser in a single location (upper left corner of the table for instance) and then try to cut each piece at each corner of the table?

If you focus the test piece in the lower right corner, will it cut properly? Likewise, does the upper left piece now fail to cut through when the focus is performed on the lower right piece?